1. Field of the Invention
The present invention relates to a hydraulic pump assembly, and more particularly to a hydraulic pump assembly comprising a hydraulic pump coupled to an oil accumulator, for supplying working oil to an actuator in a power steering device for an outboard engine.
2. Description of the Relevant Art
FIG. 3 of the accompanying drawings shows a hydraulic pump assembly 100 for supplying, when required, working oil to an actuator in a power steering device for an outboard engine. The hydraulic pump assembly 100 normally stores therein working oil under pressure so that it can be supplied from the hydraulic pump assembly 100. When required, the stored working oil is supplied to the actuator (not shown) in the power steering device. After the required working oil has been supplied or while it is being supplied, the hydraulic pump assembly 100 is replenished with the same amount of additional working oil.
More specifically, the hydraulic pump assembly 100 comprises a pump 104 drivable by an electric motor 110, and an accumulator 102. Usually, working oil is stored under high pressure in the accumulator 102. The accumulator 102, and the motor 110 and the pump 104 are housed in upper and lower spaces, respectively, in an outer shell 101. The outer shell 101 defines therein a lower oil chamber 103 which serves as an oil reservoir for storing working oil.
The accumulator 102 comprises an accumulator cylinder 105 fixedly mounted in the shell 101, a piston 106 vertically slidably fitted in the accumulator cylinder 105, and a partition 107 fixedly disposed in the cylinder 105 below the piston 106. An upper inner wall surface of the cylinder 105 and the piston 106 jointly define therebetween a gas chamber G filled with a gas under high pressure. The lower surface of the piston 106 and the upper surface of the partition 107 jointly define an oil chamber 108 therebetween. In FIG. 3, almost all working oil is supplied from the pump assembly 100 to the actuator, with the oil chamber 108 being of a substantially minimum volume.
Between the electric motor 110 and the accumulator 102, there is interposed a cap 109 which has a gear 111 for supplying working oil and an inlet pipe 112 through which the gear 111 and the lower oil chamber 103 communicate with each other. The inlet pipe 112 has a lower end disposed in the oil chamber 103. The pump 104 is composed of the cap 109 and the gear 111. When the gear 111 is driven by the motor 110, the working oil in the lower oil chamber 103 is drawn through the inlet pipe 112 by the pump 104, and forcibly supplied into the oil chamber 108 through an oil passage (not shown) defined in the cap 109.
In the shell 101, the cap 109 is surrounded by a pipe attachment 114 mounted thereon and connected to an end of an outlet pipe 113 whose discharge port 116 is connected to the actuator. An on/off valve (not shown) controlled by the power steering device is joined between the discharge port 116 and the actuator. The oil chamber 108 communicates with the on/off valve through an oil passage 109a defined in the cap 109, the pipe attachment 114, and the discharge port 116.
A controller 115 is fitted in an upper recess of the accumulator cylinder 105. The controller 115 has upper and lower sensors 115a, 115b for detecting the position of an annular magnet 106a fixedly mounted in an upper portion of an inner hole defined in the piston 106.
When the piston 106 is in its lower limit position as detected by the lower sensor 115b, the controller 115 starts to energize the electric motor 110 to forcibly supply the working oil from the lower oil chamber 103 into the oil chamber 108 of the accumulator 102. When the piston 106 reaches its upper limit position as detected by the upper sensor 115a in response to the supplied working oil, the controller 115 de-energizes the electric motor 110.
The above operation of the controller 115 is independent of operation of the on/off valve positioned downstream of the discharge port 116. Therefore, the hydraulic pump assembly 100 normally stores working oil under high pressure in the oil chamber 108, and automatically discharges the stored working oil when the on/off valve downstream of the discharge port 116 opens.
The hydraulic pump assembly 100 is of a doublewalled structure composed of the cylinder 105 of the accumulator 102 and the outer shell 101 serving as an oil tank. Accordingly, it is necessary to install the inlet pipe 112, the attachment 114, and the outlet pipe 113 within the shell 101, resulting in an increased number of components used. The double-walled structure makes the outer profile of the shell 101 larger compared with the necessary outer profile of the accumulator cylinder 105. As a consequence, the power steering device for an outboard engine is complex in structure, and large in dimensions.
The present invention has been made in view of the aforesaid problems of the conventional hydraulic pump assembly for use in a power steering device for an outboard engine.